Planar Doppler Velocimetry for Large-Scale, Low-Speed Flows

The proposed effort will extend the capabilities of Planar Doppler Velocimetry (PDV) to include flow fields 7 ft x 7 ft with a velocity resolution of 1 ft/s, providing a solution to the experimental characterization of large flow fields near parachute canopies and their wakes. The predicted improvements in velocity resolution come mainly from increased well depths of state-of-the-art CCD cameras, which enable greater photonic signal levels with an associated increase in signal-to-noise ratio. Since the use of pulsed lasers has been found to result in unacceptable speckle noise in low speed applications, the use of continuous wave lasers is proposed, which should effectively eliminate speckle noise. PDV is ideally suited to large flow fields, since the technique does not require individual seed particles to be resolved, so the observation ranges are limited only by the signal levels obtained. Several high-power, single-mode CW lasers are now available commercially that can provide large enough signals for the extended ranges needed to cover large flow fields. Investigations during Phase I will focus on refining and verifying the predictions made in this proposal of extended velocity resolution and observation range.